It's not the RAM. I'm 99% sure it's the hard drive. Get an SSD to boot your OS in and keep your 1TB for storage. If you go into task manager, you can see how much RAM you're actually using and unless it's showing that you're always using close to 4GB RAM, you won't really need to add any ram.

my older asus zonartdx audio card I had slowed down my boots times allot I would say around an average of 10 seconds, ok maybe it wasn't the card but the drivers really slowed things down.
the best thing to do is figure out what you need running and then turn off everything that you don't need running using the services I can pretty much gaurntee that you would get allof of improvements justy doing that . a good place to start is to go to the black viper web site and do some reading he has reg files ( if you like) or you could just check through what is safe to turn off and what isn't I have used that site since my windows xp days ( when windows xp first came out) I was able to figure out that I only needed ( for widnow xp at tha ttime) 12 process's running for my system to run when I was gaming in my gaming clan for enemy territory when everything was running that I needed to game like team speak irc and a couple of other things I needed to keep track of other cland I very rarely had more then 20 process's running and my system was fast .
anyways the black viper website has allot of information on it it will take some playing around though.

my laptop running that stripped down os has 33 process's running but I haven't turned off things tha tI don't need so I probably could cut down the number of process's running.